An experiment method is suggested to measure the surface spectral emissivity in field based on iterative spectrally smoth temperature emissvity separation(ISSTES) algorithm. A deliberately designed experiment is carried out to study the relationship of the spectral emissivity of soil with different grain size, different sand and water content. The results show that emissvities become lower when sand content increase and higher when water content increase in 8～9.5μm region; In 11～13μm region, the variance of emissivity is not obvious. Accordingly, a method is suggested for retrieving sand content and water content of soil with multispectral thermal infrared observation.